1. Field of the Invention
The present invention relates to a method of forming a shaped body from fine particles such as powder, whiskers or short fibers of ceramics or metals, by employing a mold having a mold chamber.
2. Description of the Prior Art
It is known to manufacture ceramic or metallic articles from fine particles of the material such as powder, whiskers or short fibers by charging a mixture of the fine particles and a fluidal binder or binding agent into a mold chamber of a mold, compacting the mixture in the mold chamber to follow the shape of the mold chamber, removing the molded body out of the mold, expelling the binding agent out of the molded body, and sintering the fine particles to form an integral body.
In the above article manufacturing processes, the fluidal biding agent has been considered to be indispensable to give a smooth fluidity to a mass of fine particles so that it is readily deformable to fill a mold chamber uniformly up to every corner thereof and also to maintain the shape of the molded body prior to the sintering of the fine particles.
However, the process of expelling the biding agent out of the molded body, which is generally to heat the molded body under ventilation of atmosphere, takes a relatively long time, and further, if the heating is not carried out at an appropriate condition, there is a high probability that an undesirable shrinkage occurs and cracks are generated.
In order to meet with these problems, it has been proposed in Japanese Patent Publication 3-9064 to use a super critical fluid as a binder remover for the mixture of fine particles and a binding agent, noting that a super critical fluid presents a high dissolubility to the biding agent due to its high density, and thus it works as a good extraction agent in expelling the binding agent out of the molded body.
Further, in Japanese Patent Publication 3-12122 it has been proposed to first replace the binding agent in the molded body by a super critical fluid and then to remove the super critical fluid from the molded body, while shifting the super critical state of the fluid directly to a gaseous state without crossing the liquid-gas border line, so that no state of coexistence of liquid and gas is encountered in the micro pores in the molded body, thereby avoiding that the micro structure of the molded body is damaged by the capillary action of the fluid in the micro bores.